This invention relates to a sheath or cannula and particularly to a cannula usable with angiographic catheters.
In certain angiographic studies, the angiographer uses a procedure known as the Desilets-Hoffman procedure to do a multiple study. This procedure is described in The American Journal of Roentgenology, Radium Therapy and Nuclear Medicine, Vol. 97, No. 2, pages 519-522, "A New Method of Percutaneous Catheterization" by Donald T. Desilets, Richard B. Hoffman and Herbert D. Ruttenberg. The angiographer obtains access to the patient's blood vessel by inserting a hollow needle through the skin and into the lumen of the blood vessel. A guidewire is passed through the needle and advanced through the artery or vein into the organ to be studied. The needle is removed leaving the guidewire in the organ. A sheath and dilator are advanced over the wire into the vessel and the dilator is removed along with the guidewire. The angiographer can then conduct the multiple studies by inserting various types of catheters into the vessel through the sheath.
In order to avoid excessive bleeding and to ensure against the possibility of an air embolism, this technique involves the physician occluding the passage through the sheath during catheter changes. When such occluding is performed manually there is always the possibility that it will not be accomplished as quickly as desired and will not be continuously effective for as long as desired. A cannula valve is disclosed in U.S. Pat. No. 4,000,739; however, it is only intended to be effective in preventing blood loss from the vessel. It is desirable that a hemostasis cannula be provided which is effective in preventing air flow into the blood vessel.